1. Field of the Invention
The present invention relates to vehicle navigation system mounted on a vehicle for navigating the vehicle to a destination, and more particularly, to a vehicle navigation system which can indicate to a driver with a display which way he should go at an intersection and/or a junction.
2. Description of Related Art
Various system for reducing the burden on drivers have been designed and mounted onto a vehicle, including a navigation system for navigating a vehicle along a predetermined route to a destination. Such a navigation system informs a driver of an appropriate direction of travel at an intersection or junction to reach the destination. In practice, an image display device is provided on an instrumental panel of the vehicle to indicate a route to the driver. For example, Japan Laid Open Utility Model (Sho)61-115298 discloses a navigation system for indicating an appropriate route to the driver by displaying it at predetermined points, such as a intersection or a short distance before a junction. By following the navigated route, the driver can reach a destination without consulting a map.
The navigation system also detects the present position of the vehicle, and both the present vehicle position and the retrieved route are displayed for guidance. The detected present position is superimposed on the pre-stored map information display, and when the vehicle approaches the intersection, an arrow or the like indicates the appropriate direction on the display including the intersection or junction. Such a navigation system is disclosed in Japan Laid Open Patent (Hei)1-173815, as well as the above Laid Open Utility Model.
The present vehicle position may be detected based on distance and direction data from a distance sensor and a direction sensor, respectively, or by detecting a radio wave from a satellite, or by a hybrid method mixing the above two concepts. However, in either method, a detection error occurs and error correction is required for detecting the present position relatively accurately. Conventionally, such error correction is made after detecting, with a steering sensor, the direction to which the vehicle is turning.
In the above described system, the present position of the vehicle is displayed in real time, and when an error occurs in the detection of the present position, the detected present position is displayed as if the vehicle has passed the intersection in spite of not having reached the intersection.
In other words, detected and displayed position does not agree with the actual present position and is displayed ahead of the actual position, because the error correction has not yet been made just before turning at the intersection. This may cause a misinterpretation by the driver.
As shown in FIGS. 1A, 1B and 1C, a gap exists between the actual position of the vehicle and the corresponding display (i.e. detected position) in a conventional system. FIG. 1A illustrates a vehicle approaching an intersection where it should turn left, FIG. 1B shows a vehicle just before the intersection, and FIG. 1C shows a vehicle which is at the intersection. In FIG. 1B, although the actual position of the vehicle is still before the intersection, the display indicates that it has already reached the intersection because of the error in detection of the present position. Further, in FIG. 1C, although the vehicle is in the middle of the intersection in reality, display shows that it has passed straight through the intersection. The driver may misrecognize that he has reached the subject intersection and may turn left (or right) at an another closer intersection.